Residual petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum are characterized by a relatively high metals, sulfur and nitrogen content. This occurs because substantially all of the contaminants present in the original crude remain in the residual fraction. Principal metal contaminants are nickel and vanadium, with iron and small amounts of copper sometimes present.
The high metals content of the residual fractions generally preclude their effective use as chargestocks for subsequent catalytic processing such as catalytic cracking and hydrocracking, because the metal contaminants deposit on the special catalysts for these processes and cause the formation of inordinate amounts of coke, dry gas and hydrogen.
It is current practice to upgrade certain residual fractions by a pyrolitic operation known as coking. In this operation the residuum is destructively distilled to produce distillates of low metals content and leave behind a solid coke fraction that contains most of the metals. Coking is typically carried out in a reactor or drum operated at about 800.degree.-1100.degree. F. temperature and a pressure of 1-10 atmospheres.
Certain residual fractions are currently subjected to visbreaking, which is a heat treatment of milder conditions than used in coking, in order to reduce their viscosity and make them more suitable as fuels. Excessive sulfur content sometimes limits the value of the product.
Presently, catalytic cracking is generally accomplished by utilizing hydrocarbon chargestocks lighter than residual fractions which usually have an API gravity less than 20. Typical cracking chargestocks are coker and/or crude unit gas oils, vacuum tower overhead, and the like, the feedstock having an API gravity from about 15 to about 45. Since these cracking chargestocks are distillates, they do not contain significant proportions of the large molecules in which the metals are concentrated. Such cracking is commonly carried out in a reactor operated at a temperature of about 800.degree.-1500.degree. F., a pressure of about 1-5 atmospheres, and a space velocity of about 1-1000 WHSV.
Metals and sulfur contaminants present similar problems with regard to hydrocracking operations which are typically carried out on chargestocks even lighter than those charged to a cracking unit. Hydrocracking catalyst is so sensitive to metals poisoning that a preliminary or first stage is often utilized for trace metals removal. Typical hydrocracking reactor conditions consist of a temperature of 400.degree.-1000.degree. F. and a pressure of 1000-3500 psig.
The economic and environmental factors relating to upgrading of petroleum residual oils and other heavy hydrocarbon feedstocks have encouraged efforts to provide improved processing technology, as exemplified by the disclosures of various United States patents.
U.S. Pat. No. 3,730,879 describes a two-bed catalyst arrangement for hydrodesulfurization of crude oil. In the first bed at least 50 percent of the total pore volume of the catalyst has pores with diameters in the 50--100 Angstrom range, and in the second bed less than 45 percent of the total pore volume of the catalyst has pores with diameters in the 50-100 Angstrom range.
U.S. Pat. No. 3,905,893 discloses a hydrodesulfurization and demetalation process which involves an initial stage having relatively high hydrogen pressure in the presence of a catalyst comprising a relatively low proportion of catalytically active hydrogenation metals. The process employs a final stage in series having a relatively lower hydrogen pressure and a catalyst comprising a relatively higher proportion of hydrogenation metals.
U.S. Pat. No. 3,901,792 describes a multi-zone method for demetalizing and desulfurizing crude oil or atmospheric residual oil. An initial contact stage contains a material having extensive macroporosity and is operated as an ebullated bed under optimum demetalation conditions. This is followed by a removal of effluent vapors and a further ebullated bed contact of the liquid with a highly active hydrodesulfurization catalyst.
U.S. Pat. No. 3,964,995 discloses a two-stage hydrodesulfurization process for a 65-80 percent desulfurization of a high metals content residuum. The first stage contains porous alumina contact material activated with at least one promoter oxide. The second stage contains a highly active desulfurization catalyst of limited porosity.
U.S. Pat. No. 3,985,643 describes an improved process for desulfurization of metals and sulfur-containing petroleum oils, which involves passing a petroleum oil through a bed of substantially aged desulfurization catalyst at a temperature not less than 770.degree. F. preceeding conventional hydrodesulfurization treatment.
U.S. Pat. No. 4,016,067 is concerned with removing metal and sulfur contaminants from petroleum oil by catalytic contact with a dual bed system. The oil is first contacted with a catalyst comprising a Group VIB metal or iron group metal oxide on an aluminum support that contains delta or theta phase alumina, the catalyst having at least 60 percent of its pore volume in pores of 100-200 Angstroms diameter, at least about 5 percent of its pore volume in pores having a diameter greater than 500 Angstroms, and a surface area up to about 110 m.sup.2 /g. The oil is then contacted with a second catalyst of the high surface area cobalt-molybdenum type.
Other U.S. patents which relate to demetalation, desulfurization and denitrification of heavy hydrocarbon oils include U.S. Pat. Nos. 2,761,816; 2,909,476; 2,921,022; 3,094,480; 3,594,312; 3,663,434; 3,696,027; 2,775,303; 3,876,530; 3,882,049; 3,897,329; and the like.
Another type of development involves the upgrading of heavy hydrocarbon oils by procedures in which at least a portion of the heavy constituents and coke precursors are converted to lower boiling hydrocarbon products, while simultaneously the concentrations of sulfur, nitrogen and metallic contaminants are reduced.
U.S. Pat. No. 4,051,015 describes a method for converting a heavy hydrocarbon oil by treatment with hydrogen in the presence of a particulate acidic copper chloride catalyst.
Other U.S. patents which relate to simultaneous decontamination and conversion of heavy hydrocarbon oils include U.S. Pat. Nos. 3,960,708; 3,989,618; 4,076,613; 4,087,348; 4,087,349; and the like, and references cited therein.
There is continuing research and development effort to improve the efficiency of processing means for upgrading of heavy hydrocarbon feedstocks.
Accordingly, it is an object of this invention to provide an improved catalytic process for reducing the metals, sulfur and nitrogen content of heavy hydrocarbon oils.
It is another object of this invention to provide a process for reducing the Conradson Carbon Residue Content of a heavy hydrocarbon oil by more than about 70 percent.
It is a further object of this invention to provide an improved process for simultaneously refining and converting a heavy hydrocarbon oil into motor fuel boiling range products in the presence of a metal halide catalyst.
Other objects and advantages of the present invention shall become apparent from the accompanying description and flow diagram.